[SPARK-5816] Add huge compatibility warning in DriverWrapper

[andrewor14]

The stability of the new submission gateway assumes that the arguments in DriverWrapper are consistent across multiple Spark versions. However, this is not at all clear from the code itself. In fact, this was broken in 20a6013, which is fortunately OK because both that commit and the original commit that added this gateway are part of the same release.

To prevent this from happening again we should at the very least add a huge warning where appropriate.

[SparkQA]

Test build #27705 has started for PR 4687 at commit 7989b56.

• This patch merges cleanly.

[SparkQA]

Test build #27705 has finished for PR 4687 at commit 7989b56.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • public class JavaFPGrowthExample
  • public class JavaPowerIterationClusteringExample
  • class Partitioner(object):
  • class SparkJobInfo(namedtuple("SparkJobInfo", "jobId stageIds status")):
  • class SparkStageInfo(namedtuple("SparkStageInfo",
  • class StatusTracker(object):

[AmplabJenkins]

Test PASSed.
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https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/27705/
Test PASSed.